A flitch is a sawn lumber plank with raw edges. These edges must be removed to produce finished lumber. Some sawmills use board edgers for this purpose. A board edger cuts the flitches lengthwise with the grain (i.e., rip sawing), removing the raw edges and splitting the remaining lumber into boards of the finished width.
Typically in modern sawmills the flitch passes through a scanner upstream of the board edger. The scanner measures the geometric shape of the flitch and sends this information the optimizer computer. The optimizer computer calculates an optimized sawing pattern for the flitch. The flitch, which is being conveyed in a transverse orientation, then passes through the saws in an orientation that produces this sawing pattern. The sawn boards are then trimmed to length in a different machine center downstream of the board edger. In a typical random length North American sawmill, the normal board lengths are 8, 10, 12, 14, 16, 18, and 20 ft. Thus the edger system can process flitch lengths of 8 to 20 feet.
However, trees are tapered from top to bottom, and in conventional edger systems the saw line must be cut along the full length of the flitch. For instance, if a flitch is wide enough for a 6″ wide board at one end and two 4″ wide boards at the other end, a conventional edger infeed system typically cuts a 6″ wide board along the full length of the flitch. This results in suboptimal recovery from the flitch. Alternatively, if the sawmill has a trimmer downstream of the edger and a mechanism to send boards back into the sawmill for remanufacture (e.g., to cut a 2×6 down to a 2×4), the conventional edger system may cut an 8″ wide board along the full length of the flitch. The flitch may then be cut into two pieces at the trimmer, and the board cut from the narrow end may be sent back to the edger to be re-cut into a narrower board. This has a negative impact on throughput, and recirculation of the boards for remanufacture requires additional equipment, floor space, and expense.